1. Field of the Invention
The present invention relates to hydraulic elevator jacks. In particular, the present invention provides a jacket-assembly and method for protecting a hydraulic elevator jack from moisture that is typically encountered when a hydraulic elevator jack is placed in contact with the ground or when a hydraulic elevator jack is used in subterranean applications. The present invention also provides an apparatus and method for alerting maintenance personnel when sufficient moisture has penetrated the jacket-assembly to start corrosion.
2. Description of Related Art
Corrosion of hydraulic elevator jacks is a significant problem because corrosion not only shortens the life of the jack but also presents a significant safety concern. A corroded elevator jack is more likely to have a catastrophic failure that can result in injury to elevator passengers and significant damage to an elevator system. Hydraulic elevator jacks are, unfortunately, often used in environments conducive to corrosion.
To combat corrosion, some elevator manufacturers have developed polyvinyl chloride (xe2x80x9cPVCxe2x80x9d) liners for their elevator jacks. While a PVC liner will protect a jack from exposure to moisture and from contact with the ground, PVC is a brittle material. For example, PVC typically has an Izod Impact resistance of between 0.5 and 1.5 ft-lbs/inch (measured in accordance with the ASTM D 256-97 protocols). Because PVC has a low Izod Impact resistance, PVC liners are susceptible to fracture and special care must be used in handling PVC liner systems. In general, hermetically sealed PVC liner systems must be installed at a jobsite because they lack the toughness and ductility to be factory-installed (i.e., installed on a jack prior to shipping it to a jobsite) and to survive the rigors of shipping and installation while on a jack. Moreover, PVC has a temperature utilization range of approximately 14xc2x0 to 140xc2x0 F., making PVC liner systems unsuitable for use in climates that have extreme high or low temperatures. A further shortcoming of prior art PVC liner systems is that they often require complicated monitoring systems to ensure that significant moisture has not breached the liner, or they require complicated means for preventing moisture from reaching the hydraulic jack.
It is thus an object of the present invention to provide a hermetically sealed jacket-assembly that effectively protects hydraulic elevator jacks from corrosion due to moisture, regardless of the source of that moisture, and that can, in one embodiment, be installed on a hydraulic elevator jack prior to shipping the jack to a jobsite where it will be installed, i.e., factory-installed on a hydraulic elevator jack. It is a further object of the present invention to provide an apparatus and method for monitoring whether moisture has breached the jacket-assembly. It is also an object of the present invention to provide an apparatus and method for testing the seal of a jacket-assembly both at the factory and in the field during and after installation.
The present invention provides a jacket-assembly and method for protecting a hydraulic elevator jack from corrosion by preventing the corrosion process from beginning. In one embodiment, the invention also provides an assembly and method for alerting elevator maintenance personnel when corrosion of a hydraulic elevator jack is imminent. Thus, the present invention eliminates the possibility of catastrophic jack failure by corrosion. In one embodiment, the present invention provides an assembly and method for isolating a hydraulic elevator jack from moisture by surrounding it with a non-corrosive, non-galvanic jacket, such as a piece of polyethylene tubing, and hermetically sealing the jacket to the jack. The invention thus isolates the hydraulic elevator jack from contact with the ground or other surfaces conducive to corrosion and electrolytic action. A moisture sensor may be inserted between the jacket and the jack. In elevator systems having sophisticated control systems, the moisture sensor may be wired to the elevator controller so that the moisture within the jacket-assembly may be monitored.
In a particular embodiment, a jacket-assembly is created by placing a jacket over a portion of a hydraulic elevator jack. The jacket is constructed of a size and shape such that when it is placed over the jack, a space will exist between the jacket and the portion of the hydraulic elevator jack. The jacket-assembly also includes a seal for hermetically sealing the jacket to the hydraulic elevator jack. The jacket is preferably manufactured from a plastic material, such as high density polyethylene, having an Izod Impact resistance of greater than 10 ft-lbs/inch (measured in accordance with method A of the ASTM D 256-97 protocols, which are hereby incorporated by reference) and preferably having a utilization temperature range of xe2x88x9250xc2x0 to 180xc2x0 F. In a particular embodiment, the jacket is made from high density polyethylene tubing having a density greater than 0.94 gms/cc, such as Chevron""s Plexco(copyright) EHMW PE 3408 or Phillips Petroleum""s Driscopipe(copyright) series 1000, which have densities of approximately 0.96 gms/cc. It, however, will be appreciated by those skilled in the art that any non-corrosive, non galvanic material can be used.
The jacket material should be sufficiently tough and ductile so that, in one embodiment, the jacket-assembly may be installed on and hermetically sealed to the hydraulic elevator jack prior to shipping it to a jobsite where it will be installed. In this regard, the material should be capable of remaining intact and hermetically sealed to the jack during shipping, handling and installation of the hydraulic elevator jack, i.e., it should be capable of being factory-installed on the jack and survive the rigors of shipping and installation without losing its ability to protect the hydraulic elevator jack. Materials having an Izod Impact resistance of greater than 10 ft-lbs/inch are particularly well suited for this application. Moreover, the material used for the jacket-assembly should have a temperature utilization of between xe2x88x9250xc2x0 and 180xc2x0 F. to allow the jacket-assembly to be used in virtually any climate where elevators may be found.
In a preferred embodiment, the jacket-assembly includes a bulkhead that is mounted on the jack and that has an outer edge with an O-ring groove. The O-ring groove accommodates an O-ring, which is used to create the hermetic seal between the jacket and the jack. A clamp, preferably installed over the upper end of the jacket, aids in creating the hermetic seal between the jacket and the O-ring and outer edge of the bulkhead. In some applications, a moisture sensor may be installed between the jack and the jacket. The moisture sensor may contain wires that pass through an orifice in the bulkhead with the aid of a wiring-harness-fitting. In sophisticated elevator systems, the moisture sensor can be wired to an elevator control panel so that it may be monitored. In other systems, the moisture sensor may be used by maintenance personnel with appropriate equipment to check whether moisture has penetrated the jacket-assembly. In some embodiments, the jacket-assembly may contain a pressure tester, comprising an air valve, to allow the hermetic seal of the jacket-assembly to be tested. The air valve may be installed in an orifice in the bulkhead.